This invention relates to circuitry and methods for detecting transitions or edges in a time-varying signal such as a serial data signal. Such edge detection may also be referred to as determining the phase of the time-varying signal (or the phase of the edges in that signal). Edge detection may be used to determine where the edge-detected signal can best be sampled to reliably recover data from that signal (e.g., by avoiding sampling in the vicinity of edges where the signal may be changing in level and therefore not stable enough for reliable sampling).
Prior Wortman et al. U.S. patent application Ser. No. 10/722,665, filed Nov. 26, 2003 (which is hereby incorporated by reference herein in its entirety) shows circuitry for determining the phase of a serial data signal so that an advantageous phase selection can be made for the clock signal that will be used to sample that signal for data recovery. The circuitry in the above-mentioned application employs circuitry for storing and recirculating data bits of a training pattern. There may be some applications in which it is desirable to avoid a need for such training-pattern-handling circuitry.